Can't reduce the idle speed

[Tailhappy]

Mums 1986 130 has had this issue for 11 years - and I really want to resolve it once and for all.

The carburettor has been replaced a few years back - and still the problem was identical. I set the idle speed using the air screw - but even screwed right in the idle is still at 900 RPM. The fuel mix is spot on - 0.9 - 1.2% CO2 and it passes the MOT every time. I am wondering if this could be a leak in the manifold gasket - or could it be something else? The carb is secure on its gaskets and there are no leaks there that I can see.

Both air and fuel O-rings are in new condition.

Thanks, Ian

[KenONeill]

Well, it could be a leak in the manifold gasket or carb mounting block: Get a piece of rubber tubing, and use it around the joints as a stethoscope.

OTOH it could also be a miscalibrated tachometer. Have you checked that agaisnt an external source?

[Tailhappy]

Well, it could be a leak in the manifold gasket or carb mounting block: Get a piece of rubber tubing, and use it around the joints as a stethoscope.

OTOH it could also be a miscalibrated tachometer. Have you checked that agaisnt an external source?

Cheers Ken,

I did check with a known good tacho (the one in the car under or over-reads depending on revs). I did renew the carb mounting block and gaskets - no change I am afraid. I will check with some rubber hose though to make sure.

[KenONeill]

It's got to be drawing extra air from someplace, and getting fuel to go with.

I'm clutching at straws a bit, but wondering about a badly assembled carb, or a leak at the primary butterfly spindle.

[Tailhappy]

It's got to be drawing extra air from someplace, and getting fuel to go with.

I'm clutching at straws a bit, but wondering about a badly assembled carb, or a leak at the primary butterfly spindle.

Ah yes, the carb spindle - never thought to check that!

[daverapid]

Assuming it's a Jikov carb check that the second choke [the one operated by vacuum] spindle isn't sticking...very common fault.

[Tailhappy]

Realised that I never gave the answer to this which I found out much later - so for anyone with this fault, it was that the carburetor was for a 136 - but had 130 jetting. Changed at some stage I suppose. I fitted a correct 130 Jikov and it idles at the correct speed.

[petergarforth]

11 hours ago, Mr105LUX said:

Realised that I never gave the answer to this which I found out much later - so for anyone with this fault, it was that the carburetor was for a 136 - but had 130 jetting. Changed at some stage I suppose. I fitted a correct 130 Jikov and it idles at the correct speed.

 

You do realise this post is nearly  9 years old???!!!😊

Edited 9 January, 2020 by petergarforth

[Tailhappy]

Yes, I realised but I hate unanswered conundrums so did not want to be guilty myself. Plus a Škoda is a long term proposition so a decade is nothing for a car like an Estelle😉

[wambobby]

does this model have the brake vacuum on the manifold? could a leak there cause a simalar problem (yeah i saw the age too)

Edited 3 February, 2020 by wambobby

[Tailhappy]

20 minutes ago, wambobby said:

does this model have the brake vacuum on the manifold? could a leak there cause a simalar problem (yeah i saw the age too)

Yes it does, but I may be in the minority, but I have never had an air leak there. I did have one in the servo once but symptoms of that were a hiss and weak brakes. But every old Skoda is different so anything is possible! 

[wambobby]

14 hours ago, Mr105LUX said:

Yes it does, but I may be in the minority, but I have never had an air leak there. I did have one in the servo once but symptoms of that were a hiss and weak brakes. But every old Skoda is different so anything is possible! 

only reason i mentioned it was when i put a rapid engine in my 110r i forgot about the manifold hole, revved up like crazy on first start